In recent years, in a road transportation system, traffic congestion is a serious problem. The economical loss arising from traffic congestion is said to be from several trillion yen to several ten trillion yen in the world as a whole.
As fundamental measures for eliminating traffic congestion, there are proposed a method in which roads of a sufficient capacity are built, and a method in which transportation are shifted to alternative transportation such as trains or airplanes. These measures, however, require a huge amount of time to see results. Further, in urban areas where traffic congestion problems are serious, it is difficult to secure land for building roads. Thus, it is difficult to implement the method in which roads of a sufficient capacity are built. Further, when the method in which transportation are shifted to alternative transportation employed, it may be difficult to obtain sufficient results, taking into consideration the climates, cultures, public security, and the like.
In view of the above, various measures for alleviating traffic congestion have been proposed by efficiently utilizing the existing roads with use of Intelligent Transport Systems (ITS). Using the ITS makes it possible to expediently obtain the results, although the results are limited, as compared with the fundament measures for eliminating traffic congestion as described above.
As a measure for alleviating traffic congestion with use of the ITS, there is a method in which vehicles are notified of traffic congestion information with use of Vehicle Information and Communication System (VICS) (registered trademark).
As another measure, there is a method in which vehicles are guided to a bypass road for bypassing a congested road where the traffic is congested when traffic congestion has occurred. According to this method, however, when vehicles bound for the congested road are simultaneously guided to the bypass road, the vehicles are concentrated on the bypass road, and traffic congestion may also occur on the bypass road.
In view of the above, in PTL 1 (JP3822424B), vehicles are guided in a time-sharing manner between a congested road and a bypass road. This makes it possible to decentralize the vehicles between the congested road and the bypass road.